Hi,

I'm thinking about the best way to handle sprites with user selected colours, this is most commonly seen in an RPG where the player can choose for example skin and hair colour and perhaps one or two clothing colours as well.

So clearly the starting point is a layered image. But I see a couple of ways to go from there. We could just store the layers separately and draw them one at a time with the appropriate colour.

Or we could try and do something clever with the fragment shader, say we bind a greyscale texture as a layer map and use this to index into an array of colours passed as a uniform. This sounds simple enough, but I have a very poor feel for whether it would actually perform better. I suppose I should just try it. One thing I don't like about it is that it would be nice to use the same shader to draw things like spell particles and projectiles which are very unlikely to have multiple layers, making this somewhat wasteful.

Also I was looking into how the old infinity engine games store their character sprites and see something interesting:

todays graphics cards have lots of memory. gigabytes of it.

one solution could be to store a color with a known value that you can reference later in the actual texture image. then at run-time if you have say 4 players, load 4 instances of the image from disk. replace the known reference color with the color of the player.

then you just draw as normal.

It looks they avoid storing the pixel layer map separately by storing it in the image hue values, the image has around 6 different hue values that are all multiples of 60 or very close.

This makes it look like a mask.

If I had to take a guess at how it worked, they probably assigned each part of the mask by dividing the color bit count (255/4 = 63.75) then retrieved this normalizing it to a black and white image then multiplied the color to the normalized mask.

The advantage of the above mask is that in theory you can have 255 separate color schemes although each scheme added would reduce the quality of every other color scheme.

Because in modern games you will almost never use more than 4 colors for a object you can just use a RGBA texture to store the mask; storing each color scheme in one channel and then multiply the color you want with the channel.

todays graphics cards have lots of memory. gigabytes of it.

one solution could be to store a color with a known value that you can reference later in the actual texture image. then at run-time if you have say 4 players, load 4 instances of the image from disk. replace the known reference color with the color of the player.

then you just draw as normal.

Yes it might be simpler to just copy the image. The only thing there is that I thought it might also be nice to be able to do more dynamic things with the mask, like with spell effects for example. You could have barkskin spell that changes the colour of the skin only, or a burning blood spell that gives the skin a pulsing glow. (I'm not sure how this would look in practice.)